SAN DIEGO (AP) — No criminal charges will be filed against any of the 42 people associated with a caravan of Central American migrants who were arrested in a clash that ended with U.S. authorities firing tear gas into Mexico to counter rock throwers, The Associated Press has learned.

The decision not to prosecute came despite President Donald Trump’s vow that the U.S. will not tolerate lawlessness and after extensive preparations were made for the caravan, including deployment of thousands of active-duty troops to the border.

Charges were not filed because the administration generally doesn’t separate families and because Customs and Border Protection didn’t collect enough evidence needed to build cases, including the names of arresting officers, according to a U.S. official familiar with the matter who was not authorized to discuss the matter publicly and spoke on condition of anonymity.

Customs and Border Protection acknowledged that no charges were filed but declined to say why.

Administration officials have portrayed the caravan as a lawless, violent mob, saying there are some 600 people in the group who have a criminal history. Homeland Security Secretary Kirstjen Nielsen said in a tweet after the Sunday clash that the actions by the migrants were “dangerous and not consistent with peacefully seeking asylum.”

Many plan to seek asylum in the U.S. but may have to wait months because the U.S. government only processes about 100 of those cases a day at the San Ysidro border crossing in San Diego.

Hundreds of people marched toward the San Ysidro crossing where they were stopped by Mexican police. They fanned out on both sides of the crossing and many slipped through an opening in the border fence or tried to climb over.

U.S. authorities say assailants threw a “hail of rocks” at agents, striking four who escaped serious injury. That prompted Border Patrol agents to launch tear gas and pepper spray balls to quell the unrest.

Rodney Scott, chief of the Border Patrol’s San Diego sector, has said those arrested Sunday for illegal entry included 27 men, with the other 15 being women and children.

Customs and Border Protection, the Border Patrol’s parent agency, referred only two cases to the Justice Department for prosecution and charges were not filed because the accused had medical problems that prevented them from being held in San Diego’s detention center, according to the U.S. official.

Many others were not referred to the Justice Department because they were children or parents accompanying children, the official said. In June, Trump retreated on the administration’s “zero-tolerance” policy on prosecuting illegal entries by generally exempting people who enter the country in families.

The other adults were not prosecuted because Customs and Border Protection didn’t have enough information to pursue charges, including the name of the arresting officers, according to the official, who said it was a chaotic scene.

U.S. authorities are working on a new system to better record evidence if similar circumstances arise in the future, the official said.

The fate of the 42 immigrants remains unclear but Customs and Border Protection said they will face deportation.

“Depending on their country of citizenship and their case’s final disposition, the Border Patrol may turn those people over to Immigration and Customs Enforcement,” said spokesman Ralph DeSio.

Lauren Mack, a spokeswoman for Immigration and Customs Enforcement, said the agency could not provide information about the immigration status of the 42 arrested without names because it doesn’t track people affiliated with the caravan.

Central Americans are typically turned over to ICE, which flies them back home. Asylum seekers are often released in the U.S. pending the outcome of their cases in immigration court.